v3.26.3
Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Details) - USD ($)
$ in Millions
Sep. 30, 2026
Dec. 31, 2025
Sep. 30, 2025
Trade Receivables, Net      
Accounts receivable $ 532.2 $ 423.9  
Allowance for doubtful receivables (0.6) (0.6)  
Receivables, net 531.6 423.3  
Inventories      
Finished products 129.2 156.1  
Work-in-process 395.5 316.7  
Raw materials 306.4 236.2  
Operating supplies 16.8 16.2  
Inventories 847.9 725.2  
Property, Plant and Equipment, Net      
Land and improvements 46.3 38.2  
Buildings and leasehold improvements 309.2 302.6  
Machinery and equipment 1,626.1 1,586.7  
Construction in progress 88.2 66.7  
Property, plant and equipment, gross 2,069.8 1,994.2  
Accumulated depreciation and amortization (929.4) (849.1)  
Land held for sale 0.0 0.1  
Property, plant and equipment, net 1,140.4 1,145.2  
Other Assets      
Restricted cash - Note 11 19.6 19.9 $ 19.8
Long-term replacement parts 36.3 28.5  
Net assets of Salaried VEBA 10.2 9.7  
Other 18.7 17.6  
Other assets 84.8 75.7  
Other Accrued Liabilities      
Uncleared cash disbursements 56.2 45.8  
Accrued income taxes and other taxes payable 10.4 7.8  
Accrued annual contribution to Salaried VEBA 0.0 2.9  
Accrued interest 10.8 6.9  
Current operating lease liabilities 5.4 4.8  
Current finance lease liabilities 3.2 2.3  
Other - Note 4 37.7 20.8  
Other accrued liabilities 123.7 91.3  
Long-Term Liabilities      
Workers' compensation accrual 24.5 26.0  
Long-term environmental accrual - Note 6 17.2 17.4  
Other long-term liabilities 41.2 38.0  
Long-term liabilities $ 82.9 $ 81.4